The proposed studies will be directed towards defining the relationship between drug sensitivity and cell cycle kinetics of CML cells and response to therapy in vivo. The sensitivity of chronic disease phase cells to busulfan and hydroxyurea and the cell cycle characteristics will be studied at the clonogenic cell level as well as at the myeloblast and promyelocyte level and the relationship between these measurements and response to therapy with these agents will be determined. With respect to blastic phase disease, for those patients who will be treated with total body irradiation plus or minus BCNU the sensitivity of the leukemic cells to these modalities will be determined as will the cell cycle characteristics. For patients in blastic phase being treated with ara C-ADR, the drug sensitivity of the patients' leukemic cells to these agents will be determined and related to treatment outcome.